WO1994028628A1 - Filtre cristallin monolithique bipolaire a etages de resonateurs disposes en parallele - Google Patents

Filtre cristallin monolithique bipolaire a etages de resonateurs disposes en parallele Download PDF

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Publication number
WO1994028628A1
WO1994028628A1 PCT/US1994/003928 US9403928W WO9428628A1 WO 1994028628 A1 WO1994028628 A1 WO 1994028628A1 US 9403928 W US9403928 W US 9403928W WO 9428628 A1 WO9428628 A1 WO 9428628A1
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WO
WIPO (PCT)
Prior art keywords
filter
resonator
substrate
stages
piezoelectric
Prior art date
Application number
PCT/US1994/003928
Other languages
English (en)
Inventor
Aristotelis Arvanitis
Original Assignee
Motorola Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Motorola Inc. filed Critical Motorola Inc.
Publication of WO1994028628A1 publication Critical patent/WO1994028628A1/fr

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Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/46—Filters
    • H03H9/54—Filters comprising resonators of piezoelectric or electrostrictive material
    • H03H9/56—Monolithic crystal filters
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/46—Filters
    • H03H9/54—Filters comprising resonators of piezoelectric or electrostrictive material
    • H03H9/542—Filters comprising resonators of piezoelectric or electrostrictive material including passive elements

Definitions

  • This invention relates to monolithic crystal filters. More particularly this invention relates to monolithic crystal filters used in radio communication circuits.
  • FIG. 1 shows a top view of a prior art two-pole monolithic crystal filter (10).
  • the filter (10) shown in FIG. 1 is comprised of a single, piezoelectric substrate (12) which is typically quartz material.
  • the upper and lower surfaces of the substrate (12) are usually planar and has on its upper surface planar electrodes (14 and 16) which comprise input and output nodes (2 and 3 respectively) of the filter (10).
  • These electrodes (14 and 16) form resonators with the addition of ground or reference electrodes (15 and 17) that are deposited on the opposite side of the substrate (12), directly below the upper surface electrodes (14 and 16).
  • the reference electrodes are shown in FIG. 1 in the broken, and dashed lines.
  • the reference potential electrodes are connected to a common reference potential node (19) which is also shown in broken lines indicating that it is on the opposite side of the substrate (12).
  • FIG. 2 shows the electrical equivalent circuit for the two-pole monolithic filter (10) shown in FIG. 1.
  • the input node in FIG. 2 is identified by reference numeral (2) and corresponds to the input node identified by the same reference numeral in FIG. 1.
  • the output node shojwn in FIG. 2 is identified by reference numeral (3) and corresponds to the output node identified by the same reference numeral in FIG. 1.
  • the reference potential node is identified in FIG. 1 and FIG. 2 by reference numeral 19.
  • the input resonator shown in FIG. 1 (comprised of electrodes 16 and 17) has an electrical equivalent shown in FIG. 2 that is comprised of a shunt capacitance (21) and a series inductance (22), a series capacitance (24) and a series resistance (26).
  • the output resonator shown in FIG. 1, (comprised of electrodes 14 and 15) has an electrical equivalent shown in FIG. 2 as series resistance (22'), series capacitance (24') and series inductance (26') and shunt capacitance (21') identify the like elements of the other resonator stage.
  • the shunt inductance (13) represents the acoustic coupling between the two resonator stages that is accomplished by means of the piezoelectric effect coupling the two resonator stages together through the substrate (12) shown in FIG. 1.
  • a problem with a two-pole monolithic piezoelectric filter, such as the device shown in FIG. 1, is that it may not provide enough signal attenuation for a particular radio frequency communications device.
  • IF intermediate frequency
  • Using four-pole or multiple two- pole devices to achieve a desired frequency rejection characteristic increases the size and cost of the filter or filters.
  • FIG. 3 there is shown a representative plot of the attenuation of a single two-pole monolithic piezoelectric filter in the plot identified by reference numeral (32).
  • a single two-pole device which may not sufficiently attenuate input signals for a particular application, for instance, in dual- conversion receivers and at twice the frequency of the second local oscillator, as shown in FIG. 3.
  • the trace shown in broken lines and identified by reference numeral (34) has a much sharper attenuation but it is at the expense of an additional two-pole of filtering and an overkill in cost, radio size and radio weight, if the only additional attenuation needed is at frequency of F c + 2F ⁇ 0 where F ⁇ 0 is the second local oscillator frequency.
  • a piezoelectric filter device that provides an improved attenuation of input signal but that requires less volume than either multiple individual two-pole or four-pole piezoelectric filters would be an improvement over the prior art.
  • FIG. 1 shows a top view of a prior art two-pole monolithic crystal piezoelectric filter.
  • FIG. 2 shows the equivalent circuit of the two-pole monolithic piezoelectric filter shown in FIG. 1.
  • FIG. 3 shows a representative plot of two-pole and four- pole piezoelectric filters.
  • FIG. 4 shows a top view of a two-pole monolithic filter and included shunt resonators on a single substrate.
  • FIG. 5 shows a plot of the attenuation of the device shown in FIG. 4.
  • FIG. 6 shows an equivalent circuit diagram of the apparatus shown in FIG. 4.
  • FIG. 7 shows a cross-sectional view of the additional shunt resonators shown in FIG. 4.
  • the objective of the piezoelectric filter is to increase the attenuation of the input signal at specific frequencies above the center frequency yet retain the bandwidth and bandwidth characteristics of the filter (31), such an increased attenuation can be accomplished by the addition of one or more shunt resonator stages at at least the input and perhaps the output of the two-pole monolithic filter shown in FIG. 6.
  • shunt resonators are of substantially higher impedance than the resonators comprising the two-pole monolithic filter (due to the smaller electrode size) and as such they do not interfere with the behavior of the pass band of the two pole filter while providing the needed attenuation at their resonance which typically is at two-times the frequency of the second local oscillator.
  • a shunt filter stage is considered to be tuned circuit coupled between the input node and ground or the reference potential.
  • Addition of a shunt filter element provides a transmission zero to the transfer function of the filter and is preferably accomplished by the addition of a resonator device on the same substrate (52) thereby precluding the need for additional filter stages that require additional volume and add parts count to a radio communications device.
  • An additional zero in the frequency response transfer function of the filter can be accomplished if an additional resonator is added to the monolithic piezoelectric quartz substrate (52) in such a way that it is not acoustically coupled into either the input resonator (56) or the output resonator (54) but yet provides a shunt path to ground of signals that are desired to be attenuated.
  • FIG. 4 there is shown an improved monolithic piezoelectric filter (50) that is comprised of a piezoelectric substrate (52).
  • This filter (50) of course has an input node identified by reference numeral (58), an output node that is identified by reference numeral (60) and a filter reference potential node identified by reference numeral (51).
  • the filter (50) has a first resonator stage or input resonator stage that includes a first signal electrode (56) and a corresponding reference potential electrode shown in FIG. 4 in broken lines and identified by reference numeral 57.
  • the first electrode (56) and its opposite and corresponding reference potential electrode (57) together comprise a piezoelectric resonator inasmuch as the substrate (52) is a piezoelectric material, typically quartz.
  • An output or second resonator stage is comprised of a second signal electrode (54) and corresponding ground or reference potential electrode shown in broken lines and identified by reference numeral (55). Together this signal electrode (54) and its electrode (55) comprise the second output resonator stage.
  • the first or input resonator stage comprised of electrodes (56 and 57) is electrically connected and coupled to the input node (58) by means of metalization deposited on to the surfaces of the electrode.
  • the output resonator stage comprised of electrodes (54 and 55) is coupled to the filter output node (60) by means of the metalization coupling the region identified by reference numeral (60) to the metalization identified by reference numeral (54 and 55).
  • the improvement in the frequency response of the filter, which response is shown in the broken line identified by reference numeral (38) and shown in FIG. 5 is accomplished by means of at least one additional resonator stage on the same substrate (52) which additional resonator is acoustically isolated from both the first and second resonator stages but electrically shunting signals at its resonance frequency, between the input node (58) and the ground or reference potential (51).
  • An additional, third resonator stage is provided on the substrate that is acoustically isolated from the first and second resonator stages by a metalization area identified by reference numeral 64 as shown. This metalization area identified by reference numeral 64 is physically opposite metalization on the under side that comprises the ground or reference potential electrode (66) as shown in FIG. 4.
  • This third resonator stage (64) is coupled to the input node (58) by means of a metalization trace identified in FIG. 4 by reference numeral 62.
  • the electrical equivalent of this third resonator stage is shown in FIG. 6 and identified by reference numeral (70). Since the metalization comprising this third resonator stage is acoustically removed from both the first and second resonator stages, it effectively provides an additional resonant circuit coupling signals of a particular frequency of interest to ground or the raw potential (51).
  • FIG. 5 there is shown a representative plot of the frequency response of the filter shown in FIG. 4 as it is modified by the addition of the two resonator stages (64 and 68). These two resonator stages will, if properly selected, provide for the increased attenuation in the region identified by reference numeral 38 (typically this frequency being at a frequency twice the frequency of the second local oscillator).
  • the frequency attenuation shown in FIG. 5 and identified by reference numeral (38), which roughly corresponds to a frequency twice that of the second local oscillator, can be such that it exceeds the attenuation provided by a four-pole filter section or two cascaded two-pole sections.
  • Reference numerals (70 and 72) identify the electrical equivalent of the resonator stages (64 and 68) shown in FIG. 4.
  • Reference numeral (51) identifies the ground potential and reference numerals (58 and 60) show the input and output terminals respectively.
  • FIG. 7 there is shown a cross-sectional view of the substrate (52) of the device shown in FIG. 4.
  • the resonator stages (64 and 68) comprised of metalization deposited into recesses formed into the substrate (52). These recesses can be formed by photo ⁇ chemical etching or other appropriate processes. Such recesses are necessary to reduce the thickness of the piezoelectric substrate; this thickness reduction will increase the unplated resonant frequency of this region of the substrate in such a way that when metalization electrodes are deposited to form resonators (64 and 68), their resonant frequencies are at or near the desired frequencies, typically a frequency substantially equal to twice the frequency of the second local oscillator, at shown in FIG. 6 and on FIG. 5.
  • Reference numerals (62 and 70) depict the metalization identified by like numerals in FIG. 4.
  • reference numeral (66) shows the metalization deposited on the under side or lower side of the substrate (52) and is the ground or reference potential for the resonator stages.

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  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Piezo-Electric Or Mechanical Vibrators, Or Delay Or Filter Circuits (AREA)

Abstract

Un filtre piézo électrique monolithique bipolaire (50) fournit une réponse en fréquence améliorée à des fréquences spécifiées au-dessus de la fréquence centrale d'un filtre bipolaire; à ces fréquences, la réponse en fréquence dépasse l'atténuation d'un filtre quadripolaire sans aucune augmentation de place, de volume ou de coût, grâce à l'adjonction d'étages de résonateurs additionnels (64 et 68) formés dans le substrat (52). Une sélection appropriée des dimensions de ces étages de résonateurs peut être utilisée pour ajuster la fréquence à laquelle ces étages de résonateurs fournissent l'atténuation additionnelle souhaitée.
PCT/US1994/003928 1993-05-24 1994-04-11 Filtre cristallin monolithique bipolaire a etages de resonateurs disposes en parallele WO1994028628A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US066,811 1993-05-24
US08/066,811 US5369382A (en) 1993-05-24 1993-05-24 Two-pole monolithic crystal filter including shunt resonator stages

Publications (1)

Publication Number Publication Date
WO1994028628A1 true WO1994028628A1 (fr) 1994-12-08

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Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5617065A (en) * 1995-06-29 1997-04-01 Motorola, Inc. Filter using enhanced quality factor resonator and method
JP2001156573A (ja) * 1999-09-17 2001-06-08 Murata Mfg Co Ltd リード付圧電部品
US7889027B2 (en) * 2005-09-09 2011-02-15 Sony Corporation Film bulk acoustic resonator shaped as an ellipse with a part cut off
US10808473B2 (en) * 2016-08-30 2020-10-20 Forum Us, Inc. Load limiting tong

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3838366A (en) * 1972-05-24 1974-09-24 Thomson Csf Monolithic electro-mechanical filters
US4013982A (en) * 1974-10-22 1977-03-22 International Standard Electric Corporation Piezoelectric crystal unit
US4287493A (en) * 1979-01-25 1981-09-01 Murata Manufacturing Co., Ltd. Piezoelectric filter
US4625138A (en) * 1984-10-24 1986-11-25 The United States Of America As Represented By The Secretary Of The Army Piezoelectric microwave resonator using lateral excitation

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4329666A (en) * 1980-08-11 1982-05-11 Motorola, Inc. Two-pole monolithic crystal filter

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3838366A (en) * 1972-05-24 1974-09-24 Thomson Csf Monolithic electro-mechanical filters
US4013982A (en) * 1974-10-22 1977-03-22 International Standard Electric Corporation Piezoelectric crystal unit
US4287493A (en) * 1979-01-25 1981-09-01 Murata Manufacturing Co., Ltd. Piezoelectric filter
US4625138A (en) * 1984-10-24 1986-11-25 The United States Of America As Represented By The Secretary Of The Army Piezoelectric microwave resonator using lateral excitation

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